Gene flow refers to the transference of genetic variation from one population to another. High rates of gene flow are known to modify the allele frequencies and reduce genetic differences among groups. Gene flow limits the process of speciation by combining gene pools form different groups. In humans, for example, it has been shown that migration in the past decreased genetic variation among their populations, thereby leading to the homogenization of genotype frequencies among geographic groups. It is for that reason that in population genetics the concept of 'human races' is now often recognized as erroneous and inadequate.
